/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.spark.repl

import java.io.{IOException, ByteArrayOutputStream, InputStream}
import java.net.{HttpURLConnection, URI, URL, URLEncoder}

import scala.util.control.NonFatal

import org.apache.hadoop.fs.{FileSystem, Path}
import org.apache.xbean.asm5._
import org.apache.xbean.asm5.Opcodes._

import org.apache.spark.{SparkConf, SparkEnv, Logging}
import org.apache.spark.deploy.SparkHadoopUtil
import org.apache.spark.util.Utils
import org.apache.spark.util.ParentClassLoader

/**
 * A ClassLoader that reads classes from a Hadoop FileSystem or HTTP URI,
 * used to load classes defined by the interpreter when the REPL is used.
 * Allows the user to specify if user class path should be first.
 * This class loader delegates getting/finding resources to parent loader,
 * which makes sense until REPL never provide resource dynamically.
 */
class ExecutorClassLoader(conf: SparkConf, classUri: String, parent: ClassLoader,
    userClassPathFirst: Boolean) extends ClassLoader with Logging {
  val uri = new URI(classUri)
  val directory = uri.getPath

  val parentLoader = new ParentClassLoader(parent)

  // Allows HTTP connect and read timeouts to be controlled for testing / debugging purposes
  private[repl] var httpUrlConnectionTimeoutMillis: Int = -1

  // Hadoop FileSystem object for our URI, if it isn't using HTTP
  var fileSystem: FileSystem = {
    if (Set("http", "https", "ftp").contains(uri.getScheme)) {
      null
    } else {
      FileSystem.get(uri, SparkHadoopUtil.get.newConfiguration(conf))
    }
  }

  override def getResource(name: String): URL = {
    parentLoader.getResource(name)
  }

  override def getResources(name: String): java.util.Enumeration[URL] = {
    parentLoader.getResources(name)
  }

  override def findClass(name: String): Class[_] = {
    userClassPathFirst match {
      case true => findClassLocally(name).getOrElse(parentLoader.loadClass(name))
      case false => {
        try {
          parentLoader.loadClass(name)
        } catch {
          case e: ClassNotFoundException => {
            val classOption = findClassLocally(name)
            classOption match {
              case None =>
                // If this class has a cause, it will break the internal assumption of Janino
                // (the compiler used for Spark SQL code-gen).
                // See org.codehaus.janino.ClassLoaderIClassLoader's findIClass, you will see
                // its behavior will be changed if there is a cause and the compilation
                // of generated class will fail.
                throw new ClassNotFoundException(name)
              case Some(a) => a
            }
          }
        }
      }
    }
  }

  private def getClassFileInputStreamFromHttpServer(pathInDirectory: String): InputStream = {
    val url = if (SparkEnv.get.securityManager.isAuthenticationEnabled()) {
      val uri = new URI(classUri + "/" + urlEncode(pathInDirectory))
      val newuri = Utils.constructURIForAuthentication(uri, SparkEnv.get.securityManager)
      newuri.toURL
    } else {
      new URL(classUri + "/" + urlEncode(pathInDirectory))
    }
    val connection: HttpURLConnection = Utils.setupSecureURLConnection(url.openConnection(),
      SparkEnv.get.securityManager).asInstanceOf[HttpURLConnection]
    // Set the connection timeouts (for testing purposes)
    if (httpUrlConnectionTimeoutMillis != -1) {
      connection.setConnectTimeout(httpUrlConnectionTimeoutMillis)
      connection.setReadTimeout(httpUrlConnectionTimeoutMillis)
    }
    connection.connect()
    try {
      if (connection.getResponseCode != 200) {
        // Close the error stream so that the connection is eligible for re-use
        try {
          connection.getErrorStream.close()
        } catch {
          case ioe: IOException =>
            logError("Exception while closing error stream", ioe)
        }
        throw new ClassNotFoundException(s"Class file not found at URL $url")
      } else {
        connection.getInputStream
      }
    } catch {
      case NonFatal(e) if !e.isInstanceOf[ClassNotFoundException] =>
        connection.disconnect()
        throw e
    }
  }

  private def getClassFileInputStreamFromFileSystem(pathInDirectory: String): InputStream = {
    val path = new Path(directory, pathInDirectory)
    if (fileSystem.exists(path)) {
      fileSystem.open(path)
    } else {
      throw new ClassNotFoundException(s"Class file not found at path $path")
    }
  }

  def findClassLocally(name: String): Option[Class[_]] = {
    val pathInDirectory = name.replace('.', '/') + ".class"
    var inputStream: InputStream = null
    try {
      inputStream = {
        if (fileSystem != null) {
          getClassFileInputStreamFromFileSystem(pathInDirectory)
        } else {
          getClassFileInputStreamFromHttpServer(pathInDirectory)
        }
      }
      val bytes = readAndTransformClass(name, inputStream)
      Some(defineClass(name, bytes, 0, bytes.length))
    } catch {
      case e: ClassNotFoundException =>
        // We did not find the class
        logDebug(s"Did not load class $name from REPL class server at $uri", e)
        None
      case e: Exception =>
        // Something bad happened while checking if the class exists
        logError(s"Failed to check existence of class $name on REPL class server at $uri", e)
        None
    } finally {
      if (inputStream != null) {
        try {
          inputStream.close()
        } catch {
          case e: Exception =>
            logError("Exception while closing inputStream", e)
        }
      }
    }
  }

  def readAndTransformClass(name: String, in: InputStream): Array[Byte] = {
    if (name.startsWith("line") && name.endsWith("$iw$")) {
      // Class seems to be an interpreter "wrapper" object storing a val or var.
      // Replace its constructor with a dummy one that does not run the
      // initialization code placed there by the REPL. The val or var will
      // be initialized later through reflection when it is used in a task.
      val cr = new ClassReader(in)
      val cw = new ClassWriter(
        ClassWriter.COMPUTE_FRAMES + ClassWriter.COMPUTE_MAXS)
      val cleaner = new ConstructorCleaner(name, cw)
      cr.accept(cleaner, 0)
      return cw.toByteArray
    } else {
      // Pass the class through unmodified
      val bos = new ByteArrayOutputStream
      val bytes = new Array[Byte](4096)
      var done = false
      while (!done) {
        val num = in.read(bytes)
        if (num >= 0) {
          bos.write(bytes, 0, num)
        } else {
          done = true
        }
      }
      return bos.toByteArray
    }
  }

  /**
   * URL-encode a string, preserving only slashes
   */
  def urlEncode(str: String): String = {
    str.split('/').map(part => URLEncoder.encode(part, "UTF-8")).mkString("/")
  }
}

class ConstructorCleaner(className: String, cv: ClassVisitor)
extends ClassVisitor(ASM5, cv) {
  override def visitMethod(access: Int, name: String, desc: String,
      sig: String, exceptions: Array[String]): MethodVisitor = {
    val mv = cv.visitMethod(access, name, desc, sig, exceptions)
    if (name == "<init>" && (access & ACC_STATIC) == 0) {
      // This is the constructor, time to clean it; just output some new
      // instructions to mv that create the object and set the static MODULE$
      // field in the class to point to it, but do nothing otherwise.
      mv.visitCode()
      mv.visitVarInsn(ALOAD, 0) // load this
      mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false)
      mv.visitVarInsn(ALOAD, 0) // load this
      // val classType = className.replace('.', '/')
      // mv.visitFieldInsn(PUTSTATIC, classType, "MODULE$", "L" + classType + ";")
      mv.visitInsn(RETURN)
      mv.visitMaxs(-1, -1) // stack size and local vars will be auto-computed
      mv.visitEnd()
      return null
    } else {
      return mv
    }
  }
}
